This invention relates to a signal recording amplifier apparatus and is suitable for an application to the recording amplifier circuit of, e.g., a data recording device for recording, particularly, information data on a magnetic tape with a rotary head.
There has in the prior art existed a data recording device for recording the information data with a high density by use of a digital video tape recorder based on a helical scan method.
More specifically, as illustrated in FIG. 1, in such a data recording device 1, the information data is coded by, e.g., an 8-9 modulation method. A record signal S0 obtained as a consequence of this coding is equalized by an equivalent circuit and at the same time amplified by a recording amplifier circuit 2. The information data is then supplied to a rotary head 4 mounted on a drum.
The drum is wound with a magnetic tape 5 to permit its running in an oblique direction. The rotary head 4 thereby scans the magnetic tape 5 by the helical scan method.
Note that the reference LS of a rotary transformer 3 designates a loss caused by the rotary transformer 3, while the reference LH of the rotary head 4 represents a total inductance of the rotary transformer 3 and the rotary head 4.
A capacity CH indicates a distributed capacity generated by the wires and the rotary transformer 3 in addition to an output capacity of the recording amplifier circuit 2 itself.
As a result, in the data recording device 1, a resonance circuit is formed by the capacity CH and the inductance LH of the head 4. In consequence, as illustrated in FIG. 2, there is produced a rise in terms of an amplitude characteristic in the vicinity of a maximum frequency f1 of a frequency characteristic T0, as seen by the solid line.
For this reason, in the data recording device 1, a dumping resistance RH, one terminal of which is grounded, is connected to an output terminal of the recording amplifier circuit 2. The frequency characteristic T1 as shown by the dashed line in FIG. 2, is thereby obtained, wherein the rise in the amplitude characteristic in the vicinity of to the maximum frequency f1 is compensated as much as possible.
According to this data recording device 1, in this manner, the information data is recorded typically at a data rate of 88 Mbps (consisting of record maximum frequency 44 MHz ). Formed on a recording track of the magnetic tape 5 is a magnetizing pattern which is reversed at the shortest interval of 0.9 .mu.m.
In this type of the data recording device 1, a rotating speed of the rotary head 4 and a running speed of the magnetic tape 5 are controlled. A relative speed between the rotary head 4 and the magnetic tape 5 in the direction of the recording track is thereby variably-controlled at a speed of 1/1, 1/2, 1/4, 1/8, 1/16 and 1/24 times respectively. Recorded are the information data having data rates 88, 44, 11, and, 3.67 Mbps , i.e., the record signals S0 having record maximum frequencies 44, 22, 11, 5.50, 2.50, and 1.84 MHz.
Namely, with respect to the information data recorded by the record signal having the record maximum frequency 44 MHz and the data rate of 88 Mbps, the relative speed between the magnetic tape 5 and the rotary head 4 in the recording track direction is variably-controlled at the speed of 1/2 times. This information data is readable as a piece of information data having the data rate 44 Mbps, i.e., the record maximum frequency of 22 MHz. A low speed reproduction at a 1/2-fold speed is thereby attainable.
Reversely, with respect to the information data recorded by the record signal S0 having the data rate 22 Mbps and the recording maximum frequency 11 MHz, the relative speed is variably-controlled at the speed of 1/1 times. The information data is readable as a piece of information data having the data rate 88 [Mbps], viz., the record maximum frequency 44 [MHz]. As a result, a high speed reproduction is thereby attainable at a 4-times speed.
As a matter of fact, in the case of the data recording device 1, a variable-speed recording is, as described above, effected at a speed of 1/1 through 1/24 times. Therefore, with respect to, e.g., observation data which varies slowly as in the case of astronomical observation, the data is recorded at a data rate as slow as 3.67 Mbps and reproduced at a data rate as high as 88 Mbps. The data is thereby efficiently analyzed in a short time by using a computer system.
In contrast with this, with respect to measurement data or observation data which varies quickly, the data is recorded at the data rate as high as 88 Mbps and reproduced at the data rate as slow as 3.67 Mbps. The data can be surely analyzed at a low speed. With this arrangement, the data recording device 1 is usable as a buffer for a frequency conversion of the information data containing a large amount of information.
In the thus constructed data recording device 1, however, the waveform-equalized record signal is amplified, or alternatively the recording signals itself contains low frequency components. Hence, a so-called linear amplifier circuit exhibiting a linear amplification characteristic is employed as the recording amplifier circuit 2. As explained above, the recording amplifier circuit 2 composed of the linear amplifier circuit includes a typically large-scale circuit. It is therefore difficult to place the circuit in close proximity to a drum on which a magnetic tape running system, such as a capstan and a guide roller, exists. In the data recording device 1, wires on the output side of the recording amplifier circuit 2 are extended.
If the wires on the output side of the recording amplifier circuit 2 are extended, a value of the distributed capacity CH increases correspondingly. In addition to the rise in the frequency characteristic T0 due to the resonance, there arises a problem in which, as expressed in the following formula, the pass frequency characteristic fH can not be extended. ##EQU1##
Such a problem becomes more conspicuous especially in the data recording device for performing multichannel recording. It is because the recording amplifier circuits corresponding to the number of channels are needed, and the wires have to be extended long corresponding thereto.